This research is aimed at uncovering the cellular mechanisms of behavioral heirarchies (choice) and associative learning in a "simple" model organism, the marine gastropod Pleurobranchaea californica. Corollary aims of the research are to determine the neural organization of the motor system that controls feeding behavior in this organism, since the feeding behavior is involved in both choice and learning. Specific projects we are undertaking are 1) a study of the synaptic organization of the feeding system in the brain of this organism; 2) an ultrastructural analysis of putative chemoreceptors (scanning and transmission electron microscopy); 3) a physiological study of chemoreception; 4) a cellular analysis of behavorial "switching" between feeding and rejection in this organism.